Cisco RV042 works in two modes for it's Dual WAN.
1. Smart Link Backup - it monitors internet connection on the primary connection. If the connection fails, it automatically connects to the secondary connection.
2. Load Balance - it provides a smarter way to distribute the internet access load. Based on our deployments, it is not the addition of the two connections but it's more of maintaining the connection speed based on the lowest WAN.
click link below for some supporting info:
Dual Internet, Load Balancing - Cisco Home Community